Amm242fission cross section

Abstract

The neutron-induced fission cross section of Am has been measured over the energy region from 10 eV to -20 MeV in a series of experiments utilizing a linac-produced "white" neutron source and a monoenergetic source of 14.1 MeV neutrons. The cross section was measured relative to that of U in the thermal (0.001 to -3 eV) and high energy (1 keV to -20 MeV) regions and normalized to the ENDF/B-V 2 5U(n, f) evaluated cross section. In the resonance energy region (0.5 eV to 10 keV) the neutron flux was measured using thin lithium glass scintillators and the relative cross section thus obtained was normalized to the thermal energy measurement. This procedure allowed a consistency check between the thermal and high energy data. The cross section data have a statistical accuracy of -0.5% at thermal energies and in the 1-MeV energy region, and a systematic uncertainty of -5%. We confirmed that Am has the largest thermal fission cross section known with a 2200 m/sec value of 6328 b. Results of a Breit-Wigner sum-of-single-levels analysis of 48 fission resonances up to 20 eV are presented and the connection of these resonance properties to the large thermal cross section is discussed. Our measurements are compared with previously reported results.

Measurement of theAm242mneutron-induced reaction cross sections

“…The 242m Am fission channel has been well studied by accelerator-based [4,[26][27][28] and detonation-based [29,30] experiments despite some discrepancies among the results [31]. For instance, the measured thermal-fission cross sections differ by ≈ 10% with quoted uncertainties of ≈ 3−5% for the experiments performed by Dabbs et al [27] and Browne et al [4].…”

“…For instance, the measured thermal-fission cross sections differ by ≈ 10% with quoted uncertainties of ≈ 3−5% for the experiments performed by Dabbs et al [27] and Browne et al [4]. These two measurements were the first experiments performed with highpurity 242m Am samples (>99%).…”

“…[33]. Due to their relatively high precision, data from Browne et al [4] and Fursov et al [28] dominate the evaluated cross section [32,33]. The electromagnetic properties of low-lying states in 242 Am were studied recently by Coulomb excitation in Ref.…”

“…These measurements differ by nearly a factor of two with quoted uncertainties of about 10 to 15%. The 242m Am(n,γ) cross section is valuable for the calculation of heavy actinide concentrations in nuclear fuel [40], actinide waste recycling, and heavy isotope production [4,41]. Also, as pointed out by Rubbia [13], the 242m Am neutron-capture cross section is important for 242m Am-based propulsion and energy systems.…”

“…Produced by 241 Am neutron capture, 242m Am is a metastable isomer of americium-242 and features the highest measured thermal-fission cross section of any known nucleus [1,2]-nearly an order of magnitude greater than the 235 U and 239 Pu thermal-fission cross sections. The high amplitude of the 242m Am thermal-fission cross section is attributed to a low-energy 242m Am(n,f) resonance, at E n,R = 0.178 eV [3], with a large neutron width [4]. With a half-life of t 1/2 = 141(2) years [5], the properties of 242m Am make it an appealing nuclear fuel.…”